1. Field of the Invention
The invention in general relates to the field of industrial lasers or other high energy systems, and more particularly to apparatus for obtaining an indication of the spatial energy density distribution of the beam generated in such apparatus.
2. Description of the Prior Art
High power lasers are utilized in industry to perform a wide variety of material processing operations such as welding, cutting, heat-treating, and surface alloying and cladding, by way of example.
Very often in such laser systems, the energy density over the entire cross section of the beam may not be uniform, and such non-uniformity may have a profound effect on the laser-processing task. Accordingly, a precise measure of the beam spatial energy distribution is of utmost importance because of its impact on consistency and repeatability with respect to, for example, the depth of penetration in welding, the speed and kerf width in cutting, temperature distribution in heat-treating, as well as other effects from laser operations.
One conventional technique to measure the spatial energy distribution of a high power laser beam utilizes a material that ablates or combusts when placed in the beam path. Material utilized in this test include wood, plexiglass and silicon brick, by way of example, and the resulting burn pattern in the material is then analyzed subjectively. This technique, although inexpensive, does not give a quantitative result but only a comparative result, in which the result may vary, depending upon the person who analyzes the pattern.
Another technique utilizes the laser to irradiate a target of suitable material and thereafter observe the secondary radiation therefrom by means of a detector, such as an infrared camera in the case of black-body radiation, or a heat-sensitive fluorescent screen, with ultraviolet sources. The accuracy and resolution of this technique are affected by the properties of the target material and the results may vary, depending upon parameters such as absorptivity, emissivity and thermal conductivity.
Scanning techniques for determining the spatial energy distribution utilize a scanning disk, blade, rod or wire to sample a portion of the beam. This technique is limited to low power lasers, which are generally less than 5 kilowatts (kW) and which do not achieve energy densities in excess of 10.sup.5 Watts/cm.sup.2. Use with higher power lasers would require an attenuating filter or other method of reducing energy density. Further, the resulting resolution with this technique is somewhat degraded because of the poor optical resolution resulting from diffraction caused by edges of the blade or wire.
A two-dimensional spatial energy distribution may be obtained with the use of an array of detectors placed in the beam path. Due to the physical size of the detectors, the spatial resolution is relatively poor and attenuating filters are required for use with higher power lasers.
The present invention is operable to precisely map the spatial energy density distribution of a high power, multi-kilowatt energy beam, such as a laser, over a two-dimensional plane perpendicular to the beam's optical axis, with a resolution heretofore unattainable.